Traditionally, the dried flower of Echium amoenum (Boraginaceae) has been used in Iran as an anxiolytic and mood enhancer. This study investigated the efficacy and safety of an aqueous extract of E. amoenum in treatment of obsessive–compulsive disorder. Forty-four patients were randomly assigned to receive either E. amoenum aqueous extract (500mg/day) or placebo in a 6-week, double blind, parallel-group trial. Patients were assessed before the study and during weeks 1, 2, 4, and 6 by the Yale-Brown Obsessive Compulsive (Y-BOCS), the Hamilton Rating Scale for Anxiety (HAM-A), and a score sheet on adverse effects. In weeks 4 and 6, the extract showed a significant superiority over placebo in reducing obsessive and compulsive and anxiety symptoms. There was no significant difference between the two groups in terms of adverse effects. The results suggest that E. amoenum aqueous extract has some anti obsessive and compulsive effects. However, further studies are needed to confirm these findings.